1. Field of the Invention
The present invention relates to a color liquid crystal display apparatus for performing a color display operation using the birefringence characteristics of a twisted-nematic liquid crystal.
2. Description of the Related Art
As a conventional display apparatus for a television set, a personal computer, an electronic portable calculator, or the like, a liquid crystal display apparatus is well known. Recently, color liquid crystal display apparatuses capable of performing a chromatic display, such as a liquid crystal color television set and the color display of a computer terminal, have been widely used.
As a color liquid crystal display apparatus, a transmission type color liquid crystal display apparatus is generally used. In this apparatus, a liquid crystal cell is sandwiched between a pair of polarizing plates, and a back light (illumination source) is disposed outside one of the polarizing plates. In this case, the liquid crystal cell is formed as follows. A pair of transparent substrates are disposed to oppose each other. Transparent electrodes are respectively formed on the opposing surfaces of the transparent substrates. A liquid crystal is then sealed between the transparent substrates. Color filters for selectively transmitting light components having specific wavelengths are disposed on one of the transparent substrates.
By ON/OFF-controlling the driving voltage applied between the pair of transparent substrates, the emergence of light from the back light is controlled. Light from the back light is selectively transmitted through each color filter in the liquid crystal display apparatus in the processing of passing therethrough. As a result, the transmitted light has a specific color. With the colored light transmitted through each color filter, a color display is performed.
A color filter, however, generally has a low transmittance. For this reason, in a color liquid crystal display apparatus using the above-mentioned color filters, the loss of transmitted light is large, resulting in a dark display. Especially, in a reflection type liquid crystal display apparatus widely used as the display portion of an electronic portable calculator or a portable device such as a wristwatch, no special light source is arranged, and light is transmitted through each color filter twice before and after reflection and undergoes optical loss. Therefore, the resultant display becomes dark. That is, it is very difficult to perform a color display operation by using color filters.
In addition, a color filter demands high precision in dimensions, e.g., thickness, and in assembly, similar to other optical elements such as a polarizing plate, resulting in an increase in cost of the liquid crystal display apparatus.
Furthermore, in a color liquid crystal display apparatus using color filters, since one pixel can display only a color corresponding to the color of a color filter arranged for this pixel, one display dot must be constituted by a plurality of pixels having color filters of different colors to display a plurality of colors. Therefore, in order to display many colors, a large number of pixels are required. As a result, the structure of the color liquid crystal display apparatus is complicated. Especially, when a multiple color display operation is to be performed by a dot matrix display type apparatus having a large number of display dots, the apparatus inevitably has a more complicated structure.